[ovs-dev] [PATCH] dpcls: Avoid one 8-byte chunk in subtable mask.

[Fischetti, Antonio]

Thanks Jarno, will create a v2.
Antonio

> -----Original Message-----
> From: Jarno Rajahalme [mailto:jarno at ovn.org]
> Sent: Wednesday, January 4, 2017 9:43 PM
> To: Fischetti, Antonio <antonio.fischetti at intel.com>
> Cc: dev at openvswitch.org; Bodireddy, Bhanuprakash
> <bhanuprakash.bodireddy at intel.com>
> Subject: Re: [PATCH] dpcls: Avoid one 8-byte chunk in subtable mask.
> 
> 
> > On Jan 4, 2017, at 6:41 AM, antonio.fischetti at intel.com wrote:
> >
> > This patch allows to skip the chunk comprising of dp_hash and in_port
> > in the subtable mask when the packet is not recirculated.  This will
> > slightly speed up the hash computation as one expensive function call
> > to hash_add64() can be skipped.
> > For each new netdev flow we wildcard in_port in the mask, so in the
> > physical case where dp_hash is also wildcarded, the resulting 8-byte
> > chunk will not be part of the subtable mask.
> >
> > The idea behind is that all the packets within a given dpcls will
> > have the same in_port value and typically dp_hash == 0.  So they will
> > have the same 8-bytes chunk in their {dp_hash, in_port} portion of the
> > miniflow. This doesn't contribute effectively in spreading hash values
> > and avoiding collisions.
> >
> > Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
> > Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
> > Co-authored-by: Bhanuprakash Bodireddy
> <bhanuprakash.bodireddy at intel.com>
> > Signed-off-by: Jarno Rajahalme <jarno at ovn.org>
> > Co-authored-by: Jarno Rajahalme <jarno at ovn.org>
> > ---
> > lib/dpif-netdev.c | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> > index 1a47a45..a808f4b 100644
> > --- a/lib/dpif-netdev.c
> > +++ b/lib/dpif-netdev.c
> > @@ -2277,8 +2277,20 @@ dp_netdev_flow_add(struct dp_netdev_pmd_thread
> *pmd,
> >     struct netdev_flow_key mask;
> >     struct dpcls *cls;
> >     odp_port_t in_port = match->flow.in_port.odp_port;
> > -
> > +    uint32_t old_odp_port;
> > +
> > +    /* As we select the dpcls based on the port number, each netdev
> flow
> > +     * belonging to the same dpcls will have the same odp_port value.
> > +     * For performance reasons here we wildcard odp_port in the mask.
> In the
> > +     * physical case where dp_hash is also wildcarded, the resulting 8-
> byte
> > +     * chunk {dp_hash, in_port} will be ignored by
> netdev_flow_mask_init() and
> > +     * will not be part of the subtable mask.
> > +     * This will speed up the hash computation during dpcls_lookup()
> because
> > +     * one call to hash_add64() will be skipped. */
> > +    old_odp_port = match->wc.masks.in_port.odp_port;
> 
> 
> Please move this line further down in the function here and do not save
> the old value:
> 
>     ovs_assert(match->wc.masks.in_port.odp_port == ODPP_NONE);
> 
> > +    match->wc.masks.in_port.odp_port = 0;
> >     netdev_flow_mask_init(&mask, match);
> > +    match->wc.masks.in_port.odp_port = old_odp_port;
> 
> And do this instead:
> 
> match->wc.masks.in_port.odp_port = ODPP_NONE;
> 
> >     /* Make sure wc does not have metadata. */
> >     ovs_assert(!FLOWMAP_HAS_FIELD(&mask.mf.map, metadata)
> >                && !FLOWMAP_HAS_FIELD(&mask.mf.map, regs));
> > --
> > 2.4.11
> >